has
    weakReferenceMap.has(key)
  
  Returns if key is in the set.
Parameters
- key 
{String}:A key to look for.
 
Returns
 {Boolean}: 
If the key exists.
weakReferenceMap.has(key)
  Returns if key is in the set.
{String}: A key to look for.
 {Boolean}: 
If the key exists.